The question of how to deal analytically with solid-solid phase transformations is considered. We can easily form the Gibbs function for each of two solid phases (homogeneous, uniform deformation) and there is a natural temptation to simply equate them in order to determine conditions under which the transformation will occur. There are a few simple geometries and morphologies for which this is legitimate, but it is not generally correct. At the other end of the "rigorous" spectrum there is the rational thermodynamics generalization of the Gibbs function (i.e., the electrochemical
tensor) and an equilibrium relationship that holds at any point on an interface between two phases under completely arbitrary conditions. However, this seems to be of limited use when trying to define global conditions for transformation. Various cases are examined to shed light on a practical question that has been around for a long time, and one that needs some quantitative examination.

While the field of shock-wave physics has provided significant insights into many of the processes related to wave propagation in materials, the exact operative micromechanisms of defect generation occurring during the shock and thereafter those controlling defect storage and damage evolution remain incompletely understood and poorly modeled. Attainment of a truly predictive capability to enable accurate simulations of dynamic impact, shock, and high-rate loading phenomena applications requires a linked experimental, modeling, and validation research program. In this talk an overview of the microstructural mechanisms affecting the strength of materials at high pressure and strain rates as well as the processes controlling damage evolution during shock loading will be reviewed. The spectrum of physical phenomena and the potential nation-wide experimental facilities poised to study them is discussed. In addition, the limitations and caveats involved in using only velocimetry, single-pass radiography, and/or shock recovery alone to elucidate the 3-D aspects of defect generation, storage, and recovery will be examined in detail. Examples of how both “real-time” and post-mortem experimental approaches are needed to quantify dislocation / defect generation, shock-induced phase transitions, and damage evolution and spallation will be discussed.

Metalized heterogeneous detonation and subsequent dense reactive particle flow have become a rapidly growing research area. Selected recent developments are reviewed with an emphasis on particle aspects in three parts: detonation-particle interactions, particle reaction and instability of particle dynamics. This includes the breakdown of the CJ detonation, detonation shock interaction
effects on wave velocity, critical failure diameter, post-combustion and particle morphology, shocked particle reaction mechanism, critical charge diameter for particle reaction, multiple heat release laws, aerodynamic fragmentation combustion, particle dynamic
instability, which leads to clustering, agglomeration and coherent jet structure, and its mechanisms through the role of stochastic particle interactions with shock waves and fluid vorticity and turbulence. These advances have laid down the fundamentals for the next stage of developments.

For the past decade, a large, interdisciplinary team at Sandia National Laboratories has been refining the Z Machine (20+ MA and 10+ MGauss) into a mature, robust, and precise platform for material dynamics experiments in the multi-Mbar pressure regime. In particular, significant effort has gone into effectively coupling condensed matter theory, magneto-hydrodynamic simulation, and electromagnetic modeling to produce a fully self-consistent simulation capability able to very accurately predict the performance of the Z machine and various experimental load configurations. This capability has been instrumental in the ability to develop experimental platforms to routinely perform magnetic ramp compression experiments to over 4 Mbar, and magnetically accelerate flyer plates to over 40 km/s, creating over 20 Mbar impact pressures. Furthermore, a strong tie has been developed between the condensed matter theory and the experimental program. This coupling has been proven time and again to be extremely fruitful, with the capability of both theory and experiment being challenged and advanced through this close interrelationship. This paper will provide an overview of the material dynamics platform and discuss several examples of the use of Z to perform extreme material dynamics studies with unprecedented accuracy in support of basic science, planetary astrophysics,
inertial confinement fusion, and the emerging field of high energy density laboratory physics.

In this work a series of experiments were carried out in which right-circular cylinders were launched into sand targets at velocities ranging from 70 to 150 m/s. The projectiles were launched along a view window in order to record the penetration event with high-speed photography. Stress measurements of the transmitted wave forms were simultaneously collected from a piezoelectric load cells buried in the sand. A particle image velocimetry
(PIV) technique, which extracted information from the photographic images, was used to resolve transmitted wave profiles. A two wave structure was observed. The first wave, a compaction wave, moves at the bulk sound speed of the sand. The second is an attached fracture wave which is stationary relative to the projectile. Together these experiments further our understanding of high-speed granular penetration events.

This paper will address the experimental results of the impact of 101.6 mm (4 in) explosively formed projectiles on normal strength concrete targets. Five projectiles were recovered using a soft recovery system to determine the average mass and nose shape of the projectiles. Velocity data for each test was measured with a high speed camera. The average projectile nose shape and mass plus the striking velocity, and the penetration depths from ten tests were compared to existing penetration equations to see if one or more of the equations is applicable for this type of projectile impact. The coarse aggregate gradation used in the concrete mix has Hugoniot data available. The Hugoniot data allows comparison of any observed spalling with the theoretical predictions.

The mechanism of penetration of the jet in silicon
carbide had been investigated experimentally and numerically. In contrast to of metals, the penetration of shaped-charge jet into ceramics has an anomalous character and a smaller depth of penetration. The penetration into ceramics is accompanied by a radial interaction of a crater wall fragments with the jet elements and this leads to a partial melting and evaporation of the elements. Appearance of a "gas" phase enables dispersion of the elements, mixing with the wall fragments, formation of an internal absorption volume, and destabilization of further part of the jet. As a result a considerable part of the jet loses the ability by the penetration.

Behind-armor debris that results from tungsten rods penetrating armor steel at 2 km/s was studied by analysis of recovered fragments. Fragment recovery was by means of particle board. Individual fragments were analyzed by x-ray tomography, which provides information for fragment identification, mass, shape, and penetration down to masses of a few milligrams. The experiments were complemented by AUTODYN and EPIC calculations. Fragments were steel or tungsten generated from the channel or from the breakout through the target rear surface. Channel fragment motions were well described by Tate theory. Breakout fragments had velocities from the projectile remnant to the channel velocity, apparently depending on where in the projectile a fragment originated. The fragment size distribution was extremely broad and did not correlate well with simple uniform-fragment-size models.

The water entry problem is considered as a classic problem which has a long research history; however, projectile water entry is still a difficult problem that has not been completely solved. In this paper, the effects of the projectile nose shape on laws of velocity attenuations for all projectiles were studied by a series of numerical simulations using the AUTODYN-2D. The result showed that the drag coefficient increases monotonically with the initial velocities for an identical projectile and decreases with the CRH values for projectiles at the same velocity. A simple and effective model was proposed to determine the relations between the drag coefficients, nose shape coefficient and initial velocities of projectiles.

This article presents the incorporation of a mechanism-based failure model into the EPIC code. The model was developed by Deshpande and Evans (DE) and is based on micromechanics and wing-crack theory. The model includes the effects of flaw size, flaw density, fracture toughness, friction,
crack shape, and crack growth rate. It is also fully 3-dimensional and covers both compression and tension. Specifically, this work incorporates the DE damage model into the Johnson-Holmquist- Beissel (JHB) ceramic
model providing a micromechanical approach for computing damage. A discussion of the DE damage model and its incorporation into the JHB model is provided. Computations are presented for two ballistic impact experiments into 99.5% - Al2O3
ceramic including some parametric effects.

Simulation of low velocity impact on structures or high velocity penetration in armor materials heavily rely on constitutive material
models.
Model constants are determined from tension, compression or torsion stress-strain at low and high strain rates at different temperatures. These model constants are required input to computer codes (LS-DYNA, DYNA3D or SPH) to accurately simulate fragment impact on structural components made of high strength 7075-T651 aluminum alloy. Johnson- Cook model constants determined for Al7075-T651 alloy bar material failed to simulate correctly the penetration into 1′ thick Al-7075-T651plates. When simulation go well beyond minor parameter tweaking and experimental results show drastically different behavior it becomes important to determine constitutive parameters from the actual material used in impact/penetration experiments. To investigate anisotropic
effects on the yield/flow stress of this alloy quasi-static and high strain rate tensile tests were performed on specimens fabricated in the longitudinal "L", transverse "T", and thickness "TH" directions of 1′ thick Al7075 Plate. While flow stress at a strain rate of ~1/s as well as ~1100/s in the thickness and transverse directions are lower than the longitudinal direction. The flow stress in the bar was comparable to flow stress in the longitudinal direction of the plate. Fracture strain data from notched tensile specimens fabricated in the L, T, and Thickness directions of 1′ thick plate are used to derive fracture constants.

When a long rod projectile hits a ceramic target, the projectile may sometimes dwell at the target boundary and flow radially. This dwell or interface defeat phenomenon has to do with the dynamic failure process of the ceramic target material. As ceramics are brittle
materials, what is needed to model dwell, is a realistic model for dynamic failure of brittle
materials. A "standard" such model is the so called JH model (which has several versions). According to JH the material accumulates damage as a function of the effective plastic strain, which is a ductile response feature. Brittle
materials are not supposed to accumulate plastic strain before they're fully failed. To model dwell we therefore propose here a different failure model. We call it BSF (= Brittle Shear Failure), and it is based on the Overstress (or overload) principle. Our BSF model is rather simple, has a small number of adjustable parameters, and is readily calibrated. We implement the model in a hydro-code and demonstrate how it works for a typical example of dwell situation. In the example, a long steel rod impacts an AD995 alumina target with and without a copper buffer.

This paper presents results from numerical simulations of a configuration in which a tungsten heavy alloy SRP penetrates a thick RHA 4340 steel at 2.6 km/s using the 2006 version of the Lagrangian
finite element code EPIC. Penetration experimental data show improved penetration efficiency by the segmented projectiles when compared to monolithic (single solid rod) projectiles. For SRP with an aspect ratio (L/D) = 1/8, a loss in penetration efficiency was seen upon successive segment impacts. The projectile configuration considered in this study was collinear impacts of eight successive discs which measured 2mm in thickness and 16mm in diameter. The EPIC simulations considered a range of parameters that influenced the Depth of Penetration (DOP) including element-particle conversion, spacing and number of segments, failure criteria, impact velocity, and mesh resolution. The EPIC results are also compared with open-literature DOP data from simulations using an Eulerian finite element code, AUTODYN for a similar configuration. In addition, the effects of back-flowing ejecta generated by the impact of first segment on the penetration processes of subsequent segments were studied in details. An alternate SRP design is proposed in this paper to alleviate the ejecta problem.

Porous-ceramic, thermal protection systems are used heavily in current reentry vehicles like the Orbiter, and they are currently being proposed for the next generation of US manned spacecraft, Orion. These systems insulate reentry critical components of a spacecraft against the intense thermal environments of atmospheric reentry. Additionally, these materials are highly exposed to space environment hazards like solid particle impacts. This paper discusses impact studies up to 10 km/s on 8 lb/ft3 alumina-fiber-enhanced-thermal-barrier (AETB8) tiles coated with a toughened-unipiece-fibrousinsulation/ reaction-cured-glass layer (TUFI/RCG). A semi-empirical, first principles impact model that describes projectile dispersion is described that provides excellent agreement with observations over a broad range of impact velocities, obliquities and projectile materials. Model extensions to look at the implications of greater than 10 GPa equation of state is also discussed. Predicted penetration probabilities for a vehicle visiting the International Space Station is 60% lower for orbital debris and 95% lower for meteoroids with this model compared to an energy scaled approach.

This article focuses on the pressure dependence and summarizes the characterization work conducted on intact and predamaged specimens of boron
carbide under confinement in a pressure vessel and in a thick steel sleeve. The failure curves obtained are presented, and the data compared to experimental data from the literature.

An explosion yielding a blast wave can cause catastrophic damage to a building and its personnel. This threat defines an immediate importance for understanding blast mitigation techniques via readily available materials. An unconfined mass of water in the form of a free flowing sheet has been experimentally tested and analyzed as a readily available mitigant. A single water sheet, with an approximate sheet thickness of 3 mm, was experimentally tested with an explosively driven shock tube at three different standoff distances. At the strongest shock strength considered, the water sheet decreased the peak overpressure of the blast wave by 80% and the impulse by 60%. Additionally, the peak overpressure transmitted through the water sheet was roughly constant regardless of standoff distance and explosive strength.

Scaled, reverse ballistic, long-rod experiments were performed at an impact velocity of ~700 m s−1. The targets were tungsten alloy rods and the projectiles either 3 or 6 mm thick rolled homogeneous armour (RHA) plates. The plate was inclined at 60° to the direction of travel and the interaction was recorded using high-speed photography, strain gauges and laser velocimetry. The pitch of the rod was varied in steps of 3° over a total range of 15°. In this range the rod deformation changed dramatically the bending process moved from a flexing of the tip away from the plate, to a marked motion into the surface. Cross comparison of the diagnostic outputs reveals the time windows for these process and also the varying sensitivity of the measurement system to that process. Post-impact recovery was also performed.